An organic EL display device which uses electroluminescence (hereinafter abbreviated to “EL”) of an organic material has attracted attention as a display device which has a higher response speed and a wider viewing angle in comparison with a liquid crystal display device.
For example, the organic EL display device is configured such that a thin film transistor (TFT) is provided on a substrate such as a glass substrate, and an organic EL element which is connected with the TFT is further provided on the substrate.
The organic EL element is a light emitting element that can emit light with high luminance by low voltage DC driving. In the organic EL element, a first electrode, an organic EL layer, and a second electrode are stacked in this order.
The organic EL layer, which is constituted by an organic compound layer including a light emitting layer, suffers property degradation by being reacted with a trace amount of moisture and oxygen. Such degradation results in loss of life to the display device. Thus, for manufacture of the organic EL display device, it is essential to form a sealing member for preventing penetration of moisture into the organic EL element.
One method of forming the sealing member is formation of a sealing film constituted by a silicon-containing film (silicon-based insulating film) which contains silicon such as silicon nitride (Si3N4) by using a chemical vapor deposition (CVD) apparatus such as a plasma CVD apparatus.
In the CVD apparatus, a film formation gas is introduced into a chamber from which air has been evacuated to generate a vacuum, and the film formation gas is then decomposed for reaction by, for example, being made into plasma between an upper electrode and a lower electrode both of which are disposed within the chamber. This forms, on a substrate disposed on the lower electrode, a film formed from a reaction product as a sealing film that covers the organic EL element.
The sealing film is formed with a pattern in any given shape for each organic EL display device by using a film formation mask so as not to cover, for example, a connection terminal between the organic EL display device and an external entity.
The reaction product is accumulated on a surface of the substrate as well as a surface of the film formation mask and others. Therefore, after the formation of the sealing film, a film formed from some portion of the reaction product which portion did not reach the substrate remains in an area of the film formation mask other than one or more openings thereof.
In view of this, after the step of forming a sealing film by use of a CVD apparatus using the film formation mask as described above, cleaning of the chamber is performed to remove the film formed from the reaction product accumulated on the area of the film formation mask other than the one or more openings thereof.
During the cleaning, exciting a cleaning gas by application of a high frequency voltage between the upper electrode and the lower electrode causes damage to the upper electrode and the lower electrode. Thus, for cleaning of the chamber, a remote plasma method is generally employed (see, for example, Non-Patent Literature 1).
In the remote plasma method, means of exciting a cleaning gas is provided outside the chamber so that the cleaning gas having been made into plasma outside the chamber is externally introduced into the chamber through the upper electrode. This causes the reaction product accumulated on the area of the film formation mask other than the one or more openings thereof to be vaporized by reaction with the cleaning gas having been made into plasma. As a result, the reaction product is removed.
As the cleaning gas, a fluorine-based gas is generally used.